U.S. patent number 6,606,214 [Application Number 09/605,155] was granted by the patent office on 2003-08-12 for system and method to minimize bearing pivot effect in disc drive actuator.
This patent grant is currently assigned to Seagate Technology LLC. Invention is credited to Kevin Arthur Gomez, Choon Kiat Lim, Joseph Cheng-Tsu Liu, Xiong Liu.
United States Patent |
6,606,214 |
Liu , et al. |
August 12, 2003 |
System and method to minimize bearing pivot effect in disc drive
actuator
Abstract
A disc drive is provided which incorporates a rotatable actuator
which is mounted to a base of the disc drive through a pivot
mechanism. The actuator positioning is controlled by a servo system
and during track following operations, the actuator arm is caused
to move. In one embodiment, the servo tracks incorporated in the
disc drive are distorted when written in by the injection of a
sinusoidal signal. In another form, the disc containing the servo
information is caused to rotate about an axis which is offset from
the disc axis. A method of creating a servo track is also
disclosed.
Inventors: |
Liu; Xiong (Singapore,
SG), Liu; Joseph Cheng-Tsu (Singapore, SG),
Lim; Choon Kiat (Singapore, SG), Gomez; Kevin
Arthur (Singapore, SG) |
Assignee: |
Seagate Technology LLC (Scotts
Valley, CA)
|
Family
ID: |
27668086 |
Appl.
No.: |
09/605,155 |
Filed: |
June 28, 2000 |
Current U.S.
Class: |
360/77.02;
360/75; 360/77.04; G9B/5.187; G9B/5.216 |
Current CPC
Class: |
G11B
5/5521 (20130101); G11B 5/596 (20130101) |
Current International
Class: |
G11B
5/596 (20060101); G11B 5/55 (20060101); G11B
005/596 (); G11B 021/02 () |
Field of
Search: |
;360/48,75,77.04,77.05,77.07,77.11,77.03 ;369/111 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sniezek; Andrew L.
Attorney, Agent or Firm: Lucente; David K. Berger; Derek
J.
Parent Case Text
This patent application claims priority from U.S. Provisional
Application No. 60/141,616 filed Jun. 30, 1999.
Claims
What is claimed is:
1. A disc drive comprising: a drivable spindle, a disc rotatably
mounted about an axis of a spindle, the disc including at least one
data storage track, a rotatable actuator assembly which is rotated
in conjunction with a pivot mechanism, the rotatable actuator
assembly includes an actuator arm and a transducer mounted on the
actuator arm; and a motor that operates the actuator assembly to
position the transducer over the at least one storage track,
wherein purposefully induced eccentricity is provided between the
at least one storage track and the axis of the spindle.
2. A disc drive according to claim 1, wherein the eccentricity is
provided by the at least one storage tack being written eccentric
to an axis of the disc.
3. A disc drive according to claim 2, wherein the at least one
storage track is written eccentric by injecting a time variable
input signal to write servo track information associated with the
at least one data storage track.
4. A disc drive according to claim 3, wherein the servo track
information is written by the actuator assembly, the actuator
assembly being movable in response to the time variable input
signal to the motor so as to cause the actuator assembly to move
during writing of the servo track information so that the at least
one data storage track is eccentric relative to the spindle
axis.
5. A disc drive according to claim 3, wherein during a track
following operation, the actuator assembly is operable to move in
response to another time varying input signal which includes a
correction signal.
6. A disc drive according to claim 1, wherein the eccentricity is
provided to minimize an effect of the pivot mechanism.
7. A disc drive according to claim 1, wherein the eccentricity
creates a continuous sinusoid in the at least one data storage
track.
8. A disc drive according to claim 7, wherein the sinusoid has a
frequency that is an integer multiple of a frequency of rotation of
the disc.
9. A disc drive according to claim 1, wherein the correction signal
is generated from the time varying input signal used in writing of
the servo track information.
10. A disc drive according to claim 1, wherein eccentricity is
provided by mounting the disc on the spindle in a position where
the at least one date storage track is eccentric to the spindle
axis.
11. A method according to claim 1, wherein the actuator arm is
caused to move through an arc during each rotation of the disc, and
wherein the arc of movement is in the range of
(2.73-8.19).times.10.sup.-3 degrees.
12. A method of retrieving data from or storing data to a data
storage track on a rotating disc of a disc drive, the method
including a step of causing a rotatable actuator assembly to pivot
about a pivot mechanism responsive to intentionally generated
eccentricity.
13. A method according to claim 12, wherein the eccentricity is
between the data storage track and a spindle axis.
14. A method according to claim 12, wherein the eccentricity is
caused by writing servo track information for the data storage
track responsive to a first time variable input signal.
15. A method according to claim 14, wherein the data storage track
is followed responsive to a second time variable input signal that
is generated from the first time variable input signal.
16. A method according to claim 12, wherein the eccentricity is
caused by mounting the disc so that the data storage track is
eccentric to a spindle axis.
17. A method for at least one of reading and writing a servo track
on a rotating disc of a disc drive, the servo track defining a
center line of a data storage track on the disc of the disc drive,
the method including steps of: providing an actuator assembly
having a transducer for at least one of reading and writing the
servo track on the rotating disc; providing a motor operatively
connected to the actuator assembly and operable to move the
transducer in response to an input signal; and providing a time
variable input signal to the motor to cause the transducer to move
during at least one of reading and writing of the servo track, the
time variable input signal associated with purposefully caused
eccentricity.
18. A method according to claim 17, wherein the time variable input
signal is periodic having a period equal to an integer multiple of
a spindle rotation frequency.
19. A method according to claim 18, wherein the periodic time
variable input signal is a sinusoid.
20. A method according to claim 17, wherein a correction signal is
generated from the time variable input signal used in writing the
servo track, wherein the correction signal is operable to be used
during operation of the disc drive in positioning of the actuator
assembly during a track following operation where the transducer is
operable to retrieve data from and store data on the data storage
track defined by the servo track.
Description
FIELD OF THE INVENTION
The present invention relates generally to disc drives and more
specifically to hard disc drives (HDD) that include rotatable
actuators.
BACKGROUND OF THE INVENTION
The rotary actuator in a HDD is typically supported by a bearing
pivot mechanism consisting of two preloaded ball bearings. The
actuator is used to position magnetic transducers (heads) over
selected information bearing tracks on the discs. The transducers
have to be positioned with great precision and the actuator
positioning is controlled by a closed loop servo system with its
movement being driven by a voice coil motor (VCM). The feedback in
the control loop is through the transducer reading servo
information pre-written on the disc. During track following or
track to track seek operations, the pivot bearing may rotate less
than one minute to as much as 20.degree. in an inner to outer
radius seek or reverse.
The friction torque generated in the bearings adversely affects the
servo control system, especially in high density track
applications. In modeling of the HDD actuator, the actuator is
often simplified as a double integrator P(s)=K/s.sup.2. However,
the non linear response of the actuator's ball bearing affects the
form of the transfer function. In particular, there is insufficient
gain at the lows frequency and the gain at the low frequency
reduces with decreasing the actuator motion. As a result of this,
the servo system is unable to handle high track density
applications with ball bearing pivot mechanisms.
Various alternatives such as knife edge type pivots have been
proposed to meet this problem. One example is disclosed in U.S.
Pat. No. 5,355,268 entitled "Disc drive knife edge pivot" by D M
Shultz, granted Oct. 11 1994. Other alternatives such as micro
actuators, or modified actuator arm designs such as that disclosed
in U.S. Pat. No. 5,166,850 entitled "Rigid, wedge-shaped mounting
structure for minimizing resonances to allow rapid transverse
movement of an attached head" have also been proposed.
A problem with such proposals is that major changes are required to
existing designs, which increase manufacturing costs and also time
to market.
SUMMARY OF THE INVENTION
The present invention provides a disc drive which includes a system
to minimize the effect of bearing friction and which may be easily
incorporated into existing disc drive designs.
In accordance with one embodiment of the invention there is
provided a disc drive which includes a rotatable disc operative to
include a plurality of data storage tracks. A rotatable actuator
assembly is mounted via a pivot mechanism to a base of the hard
disc drive and this assembly includes an actuator body and a
transducer mounted on the actuator body. A voice coil motor is
operatively connected to the actuator arm and operable to position
the transducer over a selected storage track during a track
following operation where the transducer is able to retrieve data
from, or store data on, the selected track. The radial distance
between the center line of the selected data storage track and the
spindle axis varies on angular displacement about the spindle axis
so that the actuator arm is operable to move about the pivot
mechanism during the track following operation.
In previous disc drive systems, the data storage tracks are
circular and concentric about the axis of rotation of the disc
thereby enabling the actuator arm to be stationery during the track
following operation. The center line of the data storage tracks are
typically defined by servo information which is prewritten into the
disc of the disc drive, and which is used in operation of the disc
drive by the controlling servo system. However, by maintaining the
actuator arm in motion during track following operations, it is
possible to increase the gain at the low frequency and also to
minimize the gain variation with the amplitude change of the
actuator motion. This enables the servo system associated with the
disc drive to be able to be used on discs having higher track
density applications than previously possible, using existing
designs incorporating ball bearing pivot mechanisms.
In another embodiment of the invention, there is provided a method
of retrieving data from, or storing data on, a data storage track
of a disc drive. The method includes providing a rotatable actuator
assembly which is mounted via a pivot mechanism to a base of the
disc drive and which includes an actuator body and a transducer.
The method also includes positioning the transducer over a data
storage track during a track following operation, and causing the
actuator assembly to pivot about the pivot mechanism during the
track following operation where the transducer retrieves data from,
or stores data on, the storage track.
In one form, the data storage tracks are defined to be non circular
about the disc's axis of rotation so as to cause the actuator arm
to pivot during the track following operation. This may be achieved
in different ways. In one arrangement the disc incorporates
circular data storage tracks but the disc is designed to rotate
about an axis which is offset from the central axis of the data
storage tracks. In another form, the data storage tracks are
defined to be non-circular about the axis of rotation of the disc.
This is preferably controlled by the servo information which
defines the center line of the data storage tracks which is written
in during servo track writing of the hard disc drive.
Preferably, the position of the data storage track is defined by
servo track information which is written into the disc drive. In
one form, a time varying signal is injected in during this servo
track writing. Preferably this signal is a periodic time varying
signal and the spindle rotation frequency or its harmonic
frequencies are selected as the frequency of the written in
periodic signal. In a preferred form the signal is sinusoidal.
Preferably, at the time of writing in the signal into the servo
track, a correction factor for the servo system is created and
stored and utilized by the servo system during track following
operation. Preferably, the same amplitude and phase synchronized
signal is written in for all tracks to thereby ensure that no
additional track squeeze is generated.
Preferably the amplitude of movement of the actuator arm during
track following operations is in the range of (100-300).mu." of
motion at the transducer which for a typical disc drive amounts to
[(2.73-8.19).times.10.sup.-3 ].degree. of arm rotation.
In yet a further embodiment, the present invention relates to a
method of creating a servo track on a rotating disc of a disc
drive. The method includes the steps of providing an actuator
assembly having a transducer for writing in the servo track on the
rotatable disc. A voice coil motor is operatively connected to the
actuator assembly and operable to move the transducer in response
to an input signal. The method further includes injecting a time
variable input signal to the voice coil motor to cause the
transducer to move during writing of the servo track so that the
radial distance between a center line of the servo track relative
to the axis of rotation of the disc varies on angular displacement
about the axis.
Preferably the method further includes creating a correction factor
for the servo system which is utilized by the servo system during
track following operation.
These and other features as well as advantages which characterize
the present invention will be apparent upon reading of the
following detailed description and review of the associated
drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an exploded view of a hard disc drive.
FIG. 2 is a cross-section view of the pivot bearing cartridge of
FIG. 1.
FIG. 3-5 are schematic views of the HDD illustrating the sinusoidal
signal in the servo track.
FIG. 6 is a schematic illustration of the sinusoidal signal being
written in during servo track writing.
FIG. 7 is a schematic illustration of the operation of the actuator
during track following.
FIG. 8 is a Bode plot illustrating the actuator transfer function
of prior art HDDs.
FIG. 9 is a Bode plot comparing the transfer function of existing
design with a 90 Hz sinusoid signal.
FIG. 10 is a Bode plot of the actuator transfer function with a 90
Hz sinusoid signal.
FIG. 11 is a plot comparing gain vs actuator oscillation for
different signals at 20 Hz; and
FIG. 12 is an alternative form of HDD which incorporates an offset
axis of disc rotation.
DETAILED DESCRIPTION
FIG. 1 shows a disc drive 10 in exploded view. Briefly, the disc
drive 10 includes a housing base 11 and a top cover 12, which
engage a gasket 13 to form a sealed housing that maintains a clean
environment inside the disc drive 10. A plurality of discs 14 are
mounted for rotation on a spindle motor hub 15. A plurality of
transducer heads 16 are mounted to an actuator body 17. The
actuator body 17 is adapted for pivotal motion under control of a
voice coil motor (VCM) including a voice coil 18 and magnets 19 to
controllably move a head 16 to a desired track 20 along an arcuate
path 21. Signals used to control the VCM and the heads 16 pass via
a flex circuit 22 and a connector 23 to and from electronic
circuitry on controller board 24. The controller board 24 includes
a fibre channel interface 25, a serial port connector 26 and a
spindle connector 27. The actuator assembly which includes the
actuator body 17 and transducers 16 is mounted on the base 11 via a
pivot mechanism 30, sometimes termed a pivot mechanism.
The pivot mechanism 30 (see FIG. 2) is made up of a shaft 32 on
which is mounted a housing 34 via two spaced annular ball bearing
sets 36, 38. The actuator body 17 is attached to the housing 34.
The ball bearings 36, 38 are positioned so that each exerts a small
axial force on the other. This force is known as a pre-load. It
eliminates internal clearances in the bearing sets 36, 38, but
requires careful adjustment so as to ensure adequate dynamic
properties without unacceptably increasing the frictional
resistance to rotation of the housing 34 and thus of the actuator
body 17 and transducers 16.
The discs 14 are operative to include data storage tracks which are
aligned in generally concentric rings about the spindle axis. The
center lines of the individual data storage tracks are defined by
servo information which is pre written into the disc drive and
which is read by one of the transducers 17.
The data storage tracks are closely aligned and accordingly, the
transducers must be positioned with great precision by the VCM. The
actuator 17 positioning is controlled by a closed loop servo system
having feedback generated by the transducer reading the servo
information.
In accordance with the first embodiment of the invention, the servo
tracks which are pre written in are designed to be non circular
which in turn dictates that the individual data storage tracks made
during operation of the disc drive will be non circular. In
particular, the servo track is generated by introducing a
sinusoidal signal into the actuator VCM controlling the writing the
servo information. Further the sinusoidal signal is set at a
frequency of the spindle rotation or its harmonic frequency.
Using a spindle motor rotation speed of 5,400 rpm, which is typical
of low end drives, a servo track is written in using an injected
sinusoidal signal of 90 Hz, 180 Hz and 270 Hz is illustrated in
FIGS. 3, 4 and 5 respectively.
Turning firstly to FIG. 3, the servo track 40 written in by a
standard non time variable signal is circular relative to the
spindle axis 41. When a 90 Hz sinusoidal signal is injected, the
servo track written in is caused to distort as the actuator arm is
caused to move through one cycle of the sinusoid on each single
rotation of the disc. The resulting servo track is illustrated in
FIG. 3 under reference 42.
In regard to FIG. 4, when a 180 Hz sinusoid signal is injected on
servo writing, the actuator arm is caused to move through two
cycles of the sinusoidal signal on each rotation of the disc giving
a non circular servo track 43 as shown in FIG. 4. When a 270 Hz
sinusoid is injected, the actuator arm moves through three cycles
giving servo track 44 as depicted in FIG. 5.
The amplitude of the sinusoid signal determines the arc of movement
of the actuator during servo track writing and therefore the extent
of the distortion of the servo track being written in. Preferably,
there is (100-300).mu." of motion at the transducer which is
equivalent to [2.73-8.19).times.10.sup.-3 ].degree. of arm
rotation.
FIG. 6 illustrates the process of writing in the servo track
information on to the disc drive 10.
In a typical set up, the actuator positioning is controlled by a
closed loop servo system with the movement being driven by a voice
coil motor (VCM). In this regard, an input signal 50 is injected
which determines the position of the servo track being written in
on the disc. This signal passes through servo controller 51 and
actuator power amp 52 to the VCM which in turns drives the actuator
to its designated position. An inferometer 53 incorporating a laser
54 and receiver 56 determines the precise position of the actuator
relative to a predetermined position, so as to provide the feed
back information to the servo controller to inject a correction
signal to the actuator.
To provide the required distortion to the servo track, the sinusoid
signal 58 is injected and summed to the servo corrected input
signal. In this way, the sinusoidal signal may be introduced, and
the resulting distorted non-circular servo track information may be
produced, without requiring any significant changes to the disc
drive design.
At the same time that the sinusoid signal is being written in
during servo track writing, a correction signal 59 for use in the
servo system is generated and stored, typically in a table, for
retrieval during operation of the disc drive in track following
operations.
Using a model of a hard disc drive as P(s)=k/s.sup.2, the
correction signal is defined as follows: x=y/[G*P(s)], where x
denotes the correction signal, y denotes the injected sinusoidal
signal, G is defined as the gain of power amplitude, and P(s) is
the HDD actuator model.
The correction signal is a unique value for each servo sector and
is directly used when retrieved from the table. As illustrated in
FIG. 7, the correction signal 59 is retrieved from the table and
injected as a signal to offset the amount of deviation from the
track after the sinusoidal signal has been injected so as to
correct the position of the actuator arm in use. This is achieved
when the correction signal is taken into account when the signal is
read from the table and calculations are made to ensure that the
actuator is positioned on track.
Accordingly, the system in effect overlays the existing operation
of the HDD with the injected sinusoidal signal 58 and corresponding
correction signal 59. With the introduction of these overlaid
signals, the data storage tracks follow a distorted path which
causes the actuator assembly to move during track following
operation to either store data on, or retrieve data from, the data
storage tracks of the HDD. The purpose of the movement is to
minimize the effects of friction from the pivot mechanism 30 to
enable the actuator assembly 17 to exhibit more predictable
behavior, particularly in the low frequency domain. This in turn
improves the operating performance of the servo control system
thereby enabling that system to be used for high density track
applications in conjunction with the standard pivot mechanism
configuration 30.
The improved performance of the HDD incorporating the sinusoidal
signal is evident from concept testing discussed below in
conjunction with FIGS. 9 to 11.
FIG. 8 is a Bode plot relating to testing conducted on a prior art
HDD incorporating circular data storage tracks. The Bode plot
measures Gain (dB) against the frequency supplied to the voice coil
motor under different incremental actuator arm movements; namely
1.5.mu.", 3.5.mu.", 15.mu.", 75.mu." and 188.mu.".
The Gain (dB) is the logarithm of the actuator transfer function
which is the amount of output per unit of input supplied and may be
expressed as follows: Gain
(dB)=log.vertline.(output/input).vertline. where input is the
current supplied to the voice coil motor which drives the actuator,
and output is measured in angular displacement of the arm.
Using the model of the HDD of P(s)=k/s.sup.2 the gain may be
defined as follows: Gain (dB)=20 log.vertline.P(s).vertline..
Using this model, in an ideal situation, the actuator behaves in a
manner defined by the above equation with the gain of the actuator
being directly proportional to the frequency in a linear plot.
However as illustrated from the test results displayed in the Bode
plot of FIG. 8, in reality at low frequency, the actuator response
is non linear particularly at low frequencies (ie less than 100
Hz). In particular the prior art HDD exhibits insufficient gain at
low frequency, and also the gain at the low frequency reduces with
decreasing the actuator movement.
Turning now to FIG. 9, a similar Bode plot to that of FIG. 8 is
illustrated for an actuator movement of 75.mu.". Displayed in FIG.
9 is a comparison of an existing HDD design with circular data
storage tracks against an HDD incorporating a 90 Hz injected
sinusoidal signal into the servo system. As can be seen, the HDD
which incorporates the injected sinusoidal signal exhibits
substantial increase in gain at the low frequency as compared to
the prior art design.
FIG. 10 is again a similar Bode plot to that disclosed in FIGS. 8
and 9 which illustrates the gain for the HDD incorporating a 90 Hz
sinusoidal signal for actuator movements of 75.mu." and 15.mu.". As
can be seen, the behavior of the actuator arm for the different
incremental movements of 75.mu." and 15.mu." is now far more
similar to each other than that disclosed in the prior designs as
illustrated in FIG. 8.
Finally, FIG. 11 is a comparison between the Gain (dB) at the low
frequency of 20 Hz, against the actuator oscillation which is the
amplitude of the actuator displacement expressed in micro inches
(.mu."). As shown in FIG. 11, the Gain increases as the frequency
of the injected signal increases. Furthermore, it is clear that the
Gain for higher injected frequencies is greater than the Gain from
an actuator without an injected signal. It also shows that with
each increase in the frequency of the injected signal, the plot is
shown as a decrease in gradient, thereby showing that the Gain
becomes almost constant when the injected signal is at a high
frequency such as 270 Hz.
Accordingly, by maintaining the actuator arm in motion during track
following operations, the behavior of the actuator arm when
required to move incrementally in track seek operations is
substantially more predictable as evidenced by the improvement in
Gain, especially in the low frequency domain. Further, it is
considered by the applicant that the improvements in the behavior
of the hard disc drive is contributable to the minimization of the
effects of the bearing pivot mechanism which result from
maintaining the actuator arm in motion during operation.
FIG. 12 illustrates an alternative arrangement by which the
actuator arm may be caused to move during the track following
operation. As the same components of the hard disk drive are used
in this second embodiment, like features have been given like
reference numerals.
In the embodiment of FIG. 12, the servo track is written in a
conventional form resulting in circular servo tracks which are
concentric about the axis of rotation of the disc. However, after
servo track writing, the disc 14 is laterally shifted to position
14' so that the spindle axis 41 is offset from the central axis 60
of the disc. This induced eccentricity results in a distortion in
the path of the servo track relative to the axis of rotation of the
disc 14' which in turn will cause the actuator arm to remain in
motion during track following operations. The amount of lateral
movement will determine the amplitude of movement of the arm during
track seek operations. Again, preferably there is (100-300).mu." of
motion at the transducer which is equivalent to
[(2.73-8.19).times.10.sup.-3 ].degree. of arm rotation.
Another method to describe the invention is as follows:
The present invention provides a disc drive 10 that comprises a
base 11, a spindle hub 15 on the base 11 with a number of discs
mounted rotatably about the spindle 15, where each disc has a
plurality of data storage tracks 20. The disc drive also has an
actuator assembly that is made up of a transducer 16 mounted on the
actuator arm 17, which is mounted on the base via a pivot mechanism
30. In the disc drive there is a motor, operatively connected to
the actuator assembly, such that the transducer 16 is positioned
over a selected storage track 20 during a track following operation
where the transducer 16 is able to retrieve data from, or store
data on, the selected track 20. The radial distance between the
center line of the selected data storage track and the spindle axis
41 vary on angular displacement about the spindle axis 41 so that
the actuator arm 17 is operable to move about the pivot mechanism
30 during the track following operation. The radial distance of the
center line, which is a continuous sinusoid, constantly changes on
angular displacement about the spindle axis 41 so that the actuator
arm 17 remain in motion throughout the track following operation.
The center line of each of the data storage tracks 20 on the disc
are substantially parallel to one another. During the track
following operation, the actuator arm 17 moves through an arc
during each revolution of the disc 14 such that the arc of movement
is in the range of [(2.73-8.19).times.10.sup.-3 ].degree.. The disc
drive 10 also has a servo system to control the position of the
actuator 17 with the position of the center line of the data
storage tracks 20 defined by servo track information. The servo
track information is written in on the disc 14 by the actuator
assembly prior to the operation of the disc drive 10. The actuator
assembly moves in response to a time variable input signal 50 to
the motor. This causes the actuator assembly to move during writing
in of the servo track information such that the radial distance of
the center line of the data storage track 20 relative to the
spindle axis 41 varies on angular displacement about the spindle
axis 41. During the track following operation, the actuator
assembly is operable to move in response to a time varying input
signal 50 which includes a correction signal 59 generated from the
time varying input signal 50 used in writing in of the servo track
information. The center line of the selected data storage track is
circular about a central axis 60, and the disc is mounted on the
spindle in a position where the central axis 60 is offset from the
spindle axis 41 in the range of (100-300).mu.".
In another embodiment of the invention, a method for retrieving
data from, or storing data on, a data storage track 20 on a
rotating disc 14 of a disc drive 10 is provided. The method has a
step providing a rotatable actuator assembly which is mounted to a
base 11 of a disc drive 10 via a pivot mechanism 30. The actuator
assembly is made up of a transducer 16 mounted on the actuator arm
17. The method also has a step positioning the transducer 16 over
the data storage track 20 during a track following operation.
Another step is provided to cause the actuator assembly to move
about the pivot mechanism 30 during the track following operation
where the transducer 16 retrieves data from, or stores data on, the
storage track 20. The actuator arm 17 remains in motion throughout
the track following operation and moves through an arc movement in
the range of [(2.73-8.19).times.10.sup.-3 ].degree. during each
rotation of the disc.
There is also provided a method of creating a servo track (40, 42,
43, 44) on a rotating disc 14 of a disc drive 10 where the servo
track (40, 42, 43, 44) defines the center line of a data storage
track 20 on a disc 14 of the disc drive 10. The method has a step
that provides an actuator assembly with a transducer 16 for writing
in the servo track on the rotating disc 14. Another step provides a
motor operatively connected to the actuator assembly to move the
transducer 16 in response to an input signal 50. In another step,
the motor is provided a time variable input signal 50 to cause the
transducer 16 to move during writing of the servo track (40, 42,
43, 44). This result in a radial distance between a center line of
the servo track and the axis of rotation of the disc to vary on
angular displacement about the axis. The time variable input signal
50 is periodic and sinusoidal. The period of this input signal is
equivalent to the spindle rotation frequency or a harmonic
frequency of the spindle rotation frequency. A correction signal 59
is generated from the time varying signal 50 used in writing in the
servo track. During operation of the disc drive 10, the correction
signal 59 is used to position the actuator assembly during a track
following operation where the transducer 16 retrieves data from, or
store data on, the data storage track 20 defined by the servo track
(40, 42, 43, 44).
It is to be understood that even though numerous characteristics
and advantages of various embodiments of the present invention have
been set forth in the foregoing description, together with details
of the structure and function of various embodiments of the
invention, this disclosure is illustrative only, and changes may be
made in detail, especially in matters of structure and arrangement
of parts within the principles of the present invention to the full
extent indicated by the broad general meaning of the terms in which
the appended claims are expressed. For example, the particular
elements may vary depending on the particular application for the
disc drive while maintaining substantially the same functionality
without departing from the scope and spirit of the present
invention. In addition, although the preferred embodiment described
herein is directed to a hard disc drive, it will be appreciated by
those skilled in the art that the teachings of the present
invention can be applied to other systems, without departing from
the scope and spirit of the present invention.
* * * * *